Progressive cavity pumps have been known since their invention was disclosed in U.S. Pat. No. 1,892,217, entitled "Gear Mechanism" to Moineau. The helicoidal rotor and the stator engage with each other along a sealing line to create cavities which progress axially as the rotor is rotated relative to the stator. Because of the required sealing and sliding contact concept of a Moineau pump, the stator and the rotor become subject to extensive wear, which necessitates frequent replacement of the stator and/or the rotor. Commercially available Moineau pumps, as well as those disclosed in the prior art, require extensive disassembly of the pumping apparatus to replace the worn stator and/or rotor, in addition to the down time loss of use. In a pump device, rotary motion is applied to the rotor which causes fluids and solids to be passed therethrough. Where the progressive cavity device is used as a motor, one method is to apply fluid pressure to the cavity to cause the rotor to rotate, the power therefrom having many uses. In the case of use in drilling wells, the ability to decrease the frequency of down time and extend the useful life of the motor is a desired objective.
In a progressive cavity pump or motor, problems arise because the axial centerline of the rotor is required to orbit or gyrate relative to the centerline of the stator. Thus, there is a great deal of flexture that must be accounted for to obtain long life of parts. The art is filled with various types of universal joints, flexible shafts, and mechanical connections to compensate for the orbital or gyrating type of motion. Many of these are disclosed in U.S. Pat. Nos. 4,923,376 and 2,739,650.
Heretofore, the conventional Moineau pump and motor art has used a rubber or elastomer materials bonded to steel for the stator contact surface. Such elastomers include not only natural rubber, but also synthetics, such as G.R.S., Neoprene, Butyl and Nitrile rubbers, although there are other types such as soft PVC. The key, of course, is to make the elastomer property soft enough to maintain the sealed cavity, yet be hard enough to withstand the abrasive wear from the working contact between the rotor and the stator. The rotor in these instances is usually made of steel. Some efficiency of the pump/motor is lost because the elastomer mold must be thicker at the peaks of the helicoid in order to create the progressive cavity. This lack of uniform thickness creates compressibility differences which, at increasing pressures, causes bypass of the fluids being pumped. Thus, the pump/motor reaches a point where it is less efficient at ever increasing pressure. Because of the different thicknesses, there are different expansion characteristics and different rates and the pump does more work and builds up heat from the friction.
Rubber used as the stator contact surface is not preferable in high temperature environments because of its low heat conductivity. In addition, as progressive cavity devices increase in diameter and/or length, flow characteristics to maintain a successful and long lasting bond of the rubber to a steel housing becomes more difficult. Also, where hydrocarbons make up the material to be pumped, such as in oil producing wells, rubber is known to deteriorate. One attempt to overcome these problems is taught in U.S. Pat. No. 3,912,426 by using multiple stators connected in series with separate but connected rotors for each stator. The stators surfaces, however, are still composed of rubber.
Moineau type rotor and stator devices have been used heretofore for downhole drilling motors for drilling straight or deviated boreholes in earth formations. For instance, see the following U.S. Pat. Nos.:
3,840,080 PA1 3,912,426 PA1 4,415,316 PA1 4,636,151 PA1 5,090,497 PA1 5,171,138
In applicant's prior U.S. Pat. No. 5,417,281 and copending application Ser. No. 08/637,086 composites are taught for the progressive cavity pump/motor parts and for the tubing used to carry fluids to the progressive cavity pump.
In the prior art references there is no teaching of using composites as defined herein in Moineau type motors wherein at least one of the status and rotor is comprised of a composite material. Copending application Ser. No. 08/637,086 now U.S. Pat. No. 5,759,019 teaches such use in pumps.
Composite fibers have been taught for a variety of products for their numerous characteristics of high strength, stiffness, light weight, etc., but have not been utilized successfully for use in Moineau pump/motor designs.